Cristiano Ronaldo scored an injury-time winner as Manchester United secured a 2-1 victory over Villarreal.
The Spanish side silenced Old Trafford when Paco Alcacer opened the scoring after 52 minutes.
It was deserved for Unai Emery's side, who beat United in the Europa League final last season, as they produced chance after chance in the first-half.
David De Gea was at his absolute best to deny the Yellow Submarine, making reflex saves to deny Arnaut Danjuma, Paco Alcacer and Yeremi Pino.
But the Spain international wasn't quick enough to deny Alcacer a second time as his compatriot found a gap between his legs after connecting on Danjuma's cross.
United were finding it difficult to penetrate Villarreal's staunch defence, but a moment of magic from Alex Telles evened the scores.
The Brazilian left-back, who had a poor night overall, connected from 20 yards into the bottom corner.
Of course it was Ronaldo popped up in the 94th minute to seal a vital three points, with Jesse Lingard laying off the ball before jubilant scenes erupted around Old Trafford.
The Red Devils now have three points and sit third in Group F.
Speaking after the game, Ole Gunnar Solskjaer said: "It's massive for the players, of course.
"Just to win games in this fashion, after we lost the game in Bern in that fashion, it's great. So I'd rather have a win and a defeat than two draws.
"Atalanta are a good team. Every game is hard at this level. You can see results yesterday that you don't really believe when you see them but that's European football now. The margins are so fine."
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